I thought the knowledge of the truth was knowing that we are shaped in iniquity, sinners through and through, and destined to die that way. However, Jesus death which was the sacrifice that paid for our sins, wiped the slate clean, And now we are no longer slaves to sin and the penalty of death. And that sacrifice is eternal, we just have to accept it, And put our faith in him.

Hebrews 10:26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, KJV

So if we willfully sin after being saved will it be covered by Jesus death and resurrection?

The passage is not talking about regular sins but in Matthew Henry's words it is talking about a total and final falling away.

Matthew Henry’s Concise Commentary

The sin here mentioned is a total and final falling away, when men, with a full and fixed will and resolution, despise and reject Christ, the only Saviour; despise and resist the Spirit, the only Sanctifier; and despise and renounce the gospel, the only way of salvation, and the words of eternal life. Source

John Gill's Exposition of the Bible

For if we sin wilfully

Which is not to be understood of a single act of sin, but rather of a course of sinning; nor of sins of infirmity through temptation, or even of grosser acts of sin, but of voluntary ones; and not of all voluntary ones, or in which the will is engaged and concerned, but of such which are done on set purpose, resolutely and obstinately; and not of immoral practices, but of corrupt principles, and acting according to them; it intends a total apostasy from the truth, against light and evidence, joined with obstinacy. Source

Related Passages

Hebrews 6:4-6 (New International Version)

4 It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, 5 who have tasted the goodness of the word of God and the powers of the coming age 6 and who have fallen[a] away, to be brought back to repentance. To their loss they are crucifying the Son of God all over again and subjecting him to public disgrace.

20 If they have escaped the corruption of the world by knowing our Lord and Savior Jesus Christ and are again entangled in it and are overcome, they are worse off at the end than they were at the beginning. 21 It would have been better for them not to have known the way of righteousness, than to have known it and then to turn their backs on the sacred command that was passed on to them. Source

Reasons why the willful sinning is to be understood as final falling away

1 John 2:1 NIV

My dear children, I write this to you so that you will not sin. But if anybody does sin, we have an advocate with the Father—Jesus Christ, the Righteous One. Source

One of the things Jesus is doing is that He is an Advocate mediating on our behalf. David for example sinned against God and repented.

Revelation 2:5 (New International Version)

5 Consider how far you have fallen! Repent and do the things you did at first. If you do not repent, I will come to you and remove your lampstand from its place. Source

Conclusion

Regular sins willfully done can be covered by the death of Jesus through repentance and confession. However willful sinning as in a final falling away cannot be covered.

For if we deliberately keep on sinning after receiving the knowledge
of the truth, no further sacrifice for sins is left for us

Mark 3:29 NET

But whoever blasphemes against the Holy Spirit will never be forgiven,
but is guilty of an eternal sin

Hebrews 6:6 NET

and then have committed apostasy, to renew them again to repentance,
since they are crucifying the Son of God for themselves all over again
and holding him up to contempt

These scriptures usually go hand in had. The last card to draw to an unbeliever/believer that does not want to repent, in the sense of denying Christ. Because if The Cross doesn't lead me to repent - nothing will and I'm without hope.

So if we willfully sin after being saved will it be covered by Jesus
death and resurrection?

Sin requires pastoral advice. There are as many 2nd chances as there are sins committed.
But say someone offers me a slice of pizza, to which I say 'NO thanks'.
If I respond the same way to The Cross, then how can It save me?

About willful sin.
Maybe I can't change my character but I can change my story.
Like the thief that repented and dedicated his life to give to others.
Simon persecuted and killed xtians then his story became to baptize as many souls.
Peter denied Christ Jesus then his story became to be the leader of the church.
So, in a way, willfully sinning means that I don't want to change my story.
All of this requires pastoral advice to deal with. Together with Philippians 4:13 NLT

The author uses “us” and “we” often in this chapter, so he is talking about Christians, not unbelievers. Before this verse, in the same chapter, he tells us how great is our salvation from sin. In vv11-18, we know that Jesus has taken away all sins and perfected those who have been sanctified. To those with the law written on their hearts, God will no longer remember their sins.

In vv19-25 we learn that we can come boldly to Jesus through His blood. We can come to Him in full assurance of faith. We should therefore stand fast in this hope we have of the cleansing of sin; we should exhort each other daily to be clear of sin as the day of judgment draws nearer.

Then comes this verse and those that follow, vv26-31. The author tells us that if we sin willfully after knowing these things he wrote of earlier (the “truth”), then we will not come before God with all our sins cleansed away and forgotten, but we will appear before God in our sins, and they (as shown by our shame and fearfulness), will be the proof that we have not availed ourselves of the blood of Jesus in humility, confessing our sins in fear of the judgment of God. “It is a fearful thing to fall into the hands of the living God” (11:31).

In support, Paul knew the “terror of the Lord” (2 Cor. 5:11), which is the fact that we will all stand before God, and He will judge us impartially, from the greatest to the least. So it’s important to make your “calling and election sure” (2 Peter 1:10) by the character fruit of 1:5-9, or be found of shallow faith.

These are not easy words to hear for those who have responded to the false gospel that “God loves you and has a wonderful plan for your life.” This doctrine is not a surprise to those who were saved by the gospel that all have sinned and need to flee from the wrath to come through Jesus.

According to the "law" set down by God though Moses blood sacrifice did work. This was the Jewish tradition going all the back to Abraham. The sacrifice of Gods only son ended blood sacrifices for believer in Jesus Christ.
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user40752Mar 12 '14 at 23:07

@waxeagle Animal sacrifice began in the Garden of Eden, when God gave Adam and Eve animal skins to cover their nakedness. It is not so much that the sacrifice of the animal is somehow able to atone for sin as it is that God used that to emphasize that the penalty for sin is death. That is the reason God insisted on a unblemished sacrifice. God was telling them that only their best was to be acceptable, otherwise all they would sacrifice was the worst of their herds. Since the sacrificial system was a fore shadowing of Jesus on the Cross of Calvary God taught how serious sin is to him.
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BYEMar 15 '14 at 19:54

@CecilBeckum That's what I was getting at. The idea that animal sacrifices "worked" in some way at all kind of misses the point.
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wax eagle♦Mar 16 '14 at 11:23

To all of you who wish to over complicate this passage. Remember who the author is talking, the Hebrew turned Christian. These Hebrews wanted to know if the blood sacrifice was still needed. The lines between Jews and Jews turned Christian were not as clear as they are now. The author is telling the Jew turned Christian that Jesus is the final blood sacrifice and no sacrifice of any kind is needed.